Comets

Comet McNaught glows above the mountains of Chile in this 2007 image. Experts predict that two comets could put in brilliant displays in 2013. Comets are balls of ice and rock from the outer reaches of the solar system. As they approach the Sun, some of their ice vaporizes, surrounding the comet itself with a cloud of gas and dust. Radiation and particles from the Sun push some of this material away from the comet, creating a tail that can span hundreds of thousands of miles. [ESO/H.H. Hyer]

The year’s first meteor shower should be at its best in the hours before dawn tomorrow. The Quadrantids “rain” into the atmosphere from the extinct constellation Quadrans Muralis, which is fairly close to the handle of the Big Dipper.

The Quadrantids may be the spawn of an asteroid, which in turn could be the dead remnant of a comet.

Comets are balls of frozen water and gases mixed with rock. They’re left over from the birth of the planets. In fact, the planets probably formed as many of these iceballs stuck together to form larger and larger bodies.

But hundreds of billions of iceballs remained. Many were hurled into interstellar space by the gravity of the giant planets. Others were thrown into distant orbits around the Sun. Occasionally, one of these gets a gravitational nudge — or a bump from one of its kin — and heads toward the Sun.

As it nears the Sun, some of its outer layers of ice vaporize. That releases water vapor and other gases into space, along with small grains of rock. They form a giant cloud around the comet’s nucleus. And the Sun’s radiation and magnetic field push some of this material away from the comet, forming a long, glowing tail.

As a comet loops close to the Sun, it leaves a trail of rocky debris. And if Earth happens to fly through this path, then we see a meteor shower — the calling card of a comet.

A couple of comets are expected to put on good displays in this year’s night skies. More about that tomorrow.

Script by Damond Benningfield

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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